I found a small puddle of coolant under my Formula this weekend and after doing a little investigating it appears that it is dribbling out from the thermostat area under the cap. It's dripping/misting down on to all the surrounding parts and hitting the belt, therefore spraying it all over the place and finally dripping in to a puddle on the floor. Is this just a bad cap/thermostat or something more sinister?

I recently flushed and refilled the cooling system, following the correct procedure for "burping" the air out. I haven't had any overheating problems since and the heater does work fine. However I have noticed that the fluid always remains VERY high in the thermostat housing, even when the engine is completely cold. In fact when the engine is cold and I remove the cap, about a 1/4 - 1/2 a cup of fluid always spills out. I continually check the recovery tank in the front and it goes down a little every time I drive it.

Any ideas?

If the cap is old you should replace it. The seal on mine was leaking and allowing air to seep in and coolant would flow into the overflow tank when I raised the rear of the car.
Make sure the stat handle is not hitting the cap also.
Look at the rubber seal on the cap and if you see any cracking at all replace it. They don't cost much.

Thanks for the info! Should I be concerned about the high fluid level in the thermostat housing or is that typical? Should fluid run out when I take the cap off?

The high fluid level in the thermostat housing is typical, don’t worry about it.
A small amount of fluid is normal to run out when you take the cap off.

If you hear an hssssss… when you take the cap off check for defect Coolant hoses. A defect coolant hose expands and holds pressure to the cooling system.
Maybe this explain the 1/4 - 1/2 cup of fluid spills out.

[This message has been edited by Chris_86GT (edited 05-20-2008).]

quote Originally posted by KG4ONJ: Thanks for the info! Should I be concerned about the high fluid level in the thermostat housing or is that typical? Should fluid run out when I take the cap off?

No, that's actually a good thing, no air pockets in the system and I usually lose a little bit as I pull the cap off cold.
FYI,,,, I know that we're talking about thermostat caps but if you are replacing the radiator cap remember that the auto parts stores have an incorrect listing for the part, you want a non-vented radiator cap. Just a little tidbit of information to make your life easier if you decide to replace it.

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jetman
Silver 86 SE 2M6 4-speed, with "check wallet light"
Now fortified with 8 essential slices of bacon goodness

I currently have this same problem. The seal is all cracked. Do regular auto parts stores sell the thermostat housing cap? Tks

Yes they are used on a lot of other car then Fieros. There are several other GM's that use the cap.

Another common cause for leaks at the thermostat neck is the thermostat neck itself. The lip that seals against the cap can become deformed over time. It doesn't take much to cause a bad seal. Some rust pitting in the right spot, or a slight warp, will do it.

I've dealt with this type of thing in the past. Sometimes it helps to smooth out the lip on the thermostat neck (with a sanding block and fine grit sandpaper), or to apply a light coat of grease on the rubber seal. That's assuming the rubber seal is in good shape. If the seal is cracked or damaged, you'll need to replace the cap. You should be able to find a replacement thermostat cap in your local auto parts store.